[jwmbishop]

Not sure it will work same as on engine block - but in the past I have been able to determine block number (even after milling it mostly off) by using a paint remover first to clean to bare metal, then spraying it with high spot blue, and while still wet (like within a second) wiping it with a chamois or other skin type rag (lambs skin etc). The number will "ghost" due to the displacement and work hardening of the metal during stamp impact (totally worthless with the new style etched number) - however on your door plate it may not work as the metal is softer and tin does not work herden like nickel iron (if you can drill the rivets and get the plate off cleanly - as in no bending - you may still be able to read the number on the backside in reverse - but check your state law on what you then need to do to have a legal vin plate).

I can't speak accurately of alternate locations as I have heard too many conflicting rumors of where they are - however the most prevalent seems to be top of frame rail under drivers seat - have to lift the cab to get a good clean and read.